A fluid dynamic bearing device is configured to relatively rotatably support a shaft member in a non-contact manner by a pressure (dynamic pressure generating action) of a film of an oil filled into a radial bearing gap defined between an outer peripheral surface of the shaft member and an inner peripheral surface of a bearing member. The fluid dynamic bearing device has advantages in high rotational accuracy and quietness. Thus, the fluid dynamic bearing device is preferably usable for a spindle motor incorporated in information equipment (for example, magnetic disk drives such as an HDD, drives for optical discs such as a CD-ROM, a CD-R/RW, a DVD-ROM/RAM, and a Blu-ray Disc, and drives for magneto-optical disks such as an MD and an MO), a polygon scanner motor for a laser beam printer (LBP), a color wheel for a projector, and a small-sized motor such as a fan motor to be used for a cooling fan or the like of an electrical apparatus.
As a method of manufacturing the shaft member to be used for such a fluid dynamic bearing device, for example, in JP 4504391 B2, there is described a method of grinding an outer peripheral surface of the shaft member on a grindstone while rotating the shaft member about an axial center thereof under a state in which the shaft member is sandwiched between a pair of plate members from both axial sides of the shaft member. At this time, each end surface of the shaft member and each of the plate members are held in plane-contact with each other.